Heterocyclic ureas and carbonates useful as pharmaceuticals

ABSTRACT

Compounds of formula (I), or a pharmaceutically acceptable salt thereof: ##STR1## wherein: Het is monocyclic heteroaryl having two adjacent carbon atoms, a and b, depicted in formula (I); p1 R 1  and R 2  are independently selected from hydrogen, halogen, CF 3 , C 1-6  alkyl and C 1-6  Alkoxy; 
     R 3  is hydroxy, C 1-6  alkoxy, C 3-7  alkenyl-methoxy, phenoxy or phenyl C 1-4  alkoxy in which either phenyl moiety may be substituted by one or two C 1-6  alkyl, C 1-6  alkoxy or halo; CO 2  R 6  wherein R 6  is hydrogen or C 1-6  alkyl, CONR 7  R 8  or SO 2  NR 7  R 8  wherein R 7  and R 8  are independently hydrogen or C 1-6  alkyl or together are C 4-6  polymethylene, NO 2 , (CH 2 ) m  OR 9  wherein m is 1 or 2 and R 9  is C 1-6  alkyl or S(O) n  R 10  wherein n is 0, 1 or 2 and R 10  is C 1-6  alkyl; 
     L is NH or O; 
     Z is a group of formula (a), (b) or (c); ##STR2##  wherein n is 2 or 3; p is 1 or 2; q is 1 to 3; r is 1 to 3; and R 4  or R 5  is C 1-4  alkyl; having 5-HT 3  antagonist activity, a process for their preparation and their use as pharmaceuticals.

This invention relates to novel compounds having useful pharmacological properties, to pharmaceutical compositions containing them, to a process and intermediates for their preparation, and to their use as pharmaceuticals.

GB No. 2100259A and 2125398A and EP-A-1538265 describe esters and amides having an azabicyclic side chain and possessing 5-HT₃ antagonist activity.

A class of novel, structurally distinct compounds has now been discovered. These compounds have 5-HT₃ antagonist activity.

Accordingly, the present invention provides a compound of formula (I), or a pharmaceutically acceptable salt thereof: ##STR3## wherein:

Het is monocyclic heteroaryl having two adjacent carbon atoms, a and b, depicted in formula (I);

R₁ and R₂ are independently selected from hydrogen, halogen, CF₃, C₁₋₆ alkyl and C₁₋₆ alkoxy;

R₃ is hydroxy, C₁₋₆ alkoxy, C₃₋₇ alkenyl-methoxy, phenoxy or phenyl C₁₋₄ alkoxy in which either phenyl moiety may be substituted by one or two C₁₋₆ alkyl, C₁₋₆ alkoxy or halo; CO₂ R₆ wherein R₆ is hydrogen or C₁₋₆ alkyl, CONR₇ R₈ or SO₂ NR₇ R₈ wherein R₇ and R₈ are independently hydrogen or C₁₋₆ alkyl or together are C₄₋₆ polymethylene, NO₂, (CH₂)_(m) OR₉ wherein m is 1 or 2 and R₉ is C₁₋₆ alkyl or S(O)_(n) R₁₀ wherein n is 0, 1 or 2 and R₁₀ is C₁₋₆ alkyl;

L is NH or O;

Z is a group of formula (a), (b) or (c): ##STR4## wherein n is 2 or 3; p is 1 or 2; q is 1 to 3; r is 1 to 3; and

R₄ or R₅ is C₁₋₄ alkyl.

Preferably L is NH.

Suitable values for the heteroaryl group, Het, include pyridine, pyrimidine, pyrazine, pyrrole, imidazole, thiophene, furan, oxazole or thiazole. Preferably the heteroaryl group is pyridyl, wherein the R₃ bearing carbon atom is in the 2 position and the NH bearing carbon atom is in the 3-position; or Het is thienyl (all three possible isomers).

Values for R₁ and/or R₂ include hydrogen, fluoro, chloro, bromo, CF₃, methyl, ethyl n- and iso-propyl, methoxy, ethoxy, n- and iso-propoxy. R₁ and R₂ are preferably both hydrogen.

Suitable values for alkyl groups in R₃ include methyl, ethyl, n- and iso-propyl, n-, iso-, sec- and tert-butyl; preferably methyl.

Optional halo substituents in R₃ phenoxy or phenyl-C₁₋₄ alkoxy include fluoro, chloro and bromo.

Preferred examples of R₃ include methoxy, ethoxy, propoxy, methoxycarbonyl, ethoxycarbonyl and dimethylaminosulphonyl.

L is often NH.

Preferably n is 2 and p, q and r are independently 1 or 2.

Examples of R₄ /R₅ include as groups of interest C₁₋₃ -alkyl such as methyl, ethyl and n- and iso-propyl.

R₄ /R₅ is preferably methyl or ethyl, most preferably methyl.

The pharmaceutically acceptable salts of the compounds of the formula (I) include acid addition salts with conventional acids such as hydrochloric, hydrobromic, boric, phosphoric, sulphuric acids and pharmaceutically acceptable organic acids such as acetic, tartaric, maleic, citric, succinic, benzoic, ascorbic, methanesulphonic, α-keto glutaric, α-glycerophosphoric, and glucose-1-phosphoric acids.

The pharmaceutically acceptable salts of the compounds of the formula (I) are usually acid addition salts with acids such as hydrochloric, hydrobromic, phosphoric, sulphuric, citric, tartaric, lactic and acetic acid.

Preferably the acid addition salt is the hydrochloride salt.

Examples of pharmaceutically acceptable salts include quaternary derivatives of the compounds of formula (I) such as the compounds quaternised by compounds R_(a) -T wherein R_(a) is C₁₋₆ alkyl, phenyl-C₁₋₆ alkyl or C₅₋₇ cycloalkyl, and T is a radical corresponding to an anion of an acid. Suitable examples of R_(a) include methyl, ethyl and n- and iso-propyl; and benzyl and phenethyl. Suitable examples of T include halide such as chloride, bromide and iodide.

Examples of pharmaceutically acceptable salts also include internal salts such as N-oxides.

The compounds of the formula (I), their pharmaceutically acceptable salts, (including quaternary derivatives and N-oxides) may also form pharmaceutically acceptable solvates, such as hydrates, which are included wherever a compound of formula (I) or a salt thereof is herein referred to.

It will of course be realised that some of the compounds of the formula (I) have chiral or prochiral centres and thus are capable of existing in a number of stereoisomeric forms including enantiomers. The invention extends to each of these stereoisomeric forms (including enantiomers), and to mixtures thereof (including racemates). The different stereoisomeric forms may be separated one from the other by the usual methods.

It will also be realised that compounds of formula (I) may adopt an endo or exo configuration with respect to L. The endo configuration is preferred.

A group of compounds within formula (I) is of formula (II): ##STR5## wherein the variables are as defined in formula (I).

Examples of the variables and preferred variables are as so described for corresponding variables in relation to formula (I).

A further group of compounds within formula (I) is of formula (III): ##STR6## wherein q¹ is 1 or 2 and the remaining variables are as defined in formula (I).

Examples of the variables and preferred variables are as so described for the corresponding variables in formula (I).

There is a further group of compounds within formula (I) of formula (IV): ##STR7## wherein r¹ is 1 or 2 and the remaining variables are as defined in formula (I).

Examples of the variables and preferred variables are so described as the corresponding variables in formula (I).

The invention also provides a process for the preparation of a compound of formula (I), or a pharmaceutically acceptable salt thereof, which process comprises reacting a compound of formula (V): ##STR8## with a compound of formula (VI):

    J--Z.sup.1                                                 (VI)

wherein

Y is hydrogen and G is COQ₁ where Q₁ is a leaving group; or G and Y together are ═C═O; or G is hydrogen (when Y is hydrogen); and, when G is COQ₁ or G--N--Y is N═C═O, J is NH₂, or OH or a reactive derivative thereof or, when G is hydrogen, J is a group containing an activated carbonyl group capable of forming a CO--L-- linkage with the compound of formula (V); Z¹ is Z as defined or Z wherein R₄ /R₅ is replaced by a hydrogenolysable protecting group; and the remaining variables are as hereinbefore defined; and thereafter optionally converting any R₁, R₂ and/or R₃ group to another R₁, R₂ and/or R₃ group respectively, converting Z¹, when other than Z, to Z; and optionally forming a pharmaceutically acceptable salt of the resultant compound of formula (I).

Examples of leaving groups Q₁, displaceable by a nucleophile, include halogen such as chloro and bromo, C₁₋₄ alkoxy, such as CH₃ O and C₂ H₅ O--, PhO-- or activated hydrocarbyloxy, such as Cl₅ C₆ O-- or Cl₃ CO--.

If a group Q₁ is halide, then the reaction is preferably carried out at non-extreme temperatures in an inert non-hydroxylic solvent, such as benzene, dichloromethane, toluene, diethyl ether, tetrahydrofuran (THF) or dimethylformamide (DMF). It is also preferably carried out in the presence of an acid acceptor, such as an organic base, in particular a tertiary amine, such as triethylamine, trimethylamine, pyridine or picoline, some of which can also function as the solvent. Alternatively, the acid acceptor can be inorganic, such as calcium carbonate, sodium carbonate or potassium carbonate. Temperatures of 0°-100° C., in particular 10°-80° C. are suitable.

If a group Q₁ is C₁₋₄ alkoxy, phenoxy or activated hydrocarbyloxy then the reaction is preferably carried out in an inert polar solvent, such as toluene or dimethylformamide. It is also preferred that the group Q₁ is Cl₃ CO-- and that the reaction is carried out in toluene at reflux temperature.

In a preferred process variant, G and Y together are ═C═O in which case the reaction takes place in an inert solvent, such as ether or toluene, at 0°-100° C., preferably ambient temperature.

When L is OH or a reactive derivative thereof, the reactive derivative is often a salt, such as the lithium, sodium or potassium salt.

When G is hydrogen, J--Z¹ may be a compound of formula (VII) or (VIII) when L is NH; or of formula (IX) when L is O: ##STR9## wherein

Z¹ is hereinbefore defined, and Q₂ and Q₃ are leaving groups, preferably Cl₃ CO and Cl respectively.

When J--Z¹ is of formula (VII), the reaction is preferably carried out in an inert solvent, under conventional conditions 0°-100° C.

Q₂ is a leaving group as defined for Q₁ hereinafter; and the reaction is carried out in accordance with the conditions described herein for the reaction wherein G is COQ₁.

Examples of Q₃, displaceable by a nucleophile, include halogen, such as chloro and bromo; and activated hydrocarbyloxy, such as Cl₅ C₆ O-- and Cl₃ CO.

If a group Q₃ is a halide, the reaction is carried out as described above for Q₁ halide.

If Q₃ is activated hydrocarbyloxy, the reaction is carried out as described for Q₁ activated hydrocarbyloxy.

It will be apparent that compounds of the formula (I) containing an R₁ or R₂ group which is convertible to another R₁ or R₂ group are useful novel intermediates. For example, a hydrogen substituent is convertible to a halogen substituent by halogenation using conventional halogenating agents.

Compounds of formula (I) wherein R₃ is CO₂ H may be converted to compounds of formula (I) wherein R₃ is CO₂ R₆ ¹ wherein R₆ ¹ is C₁₋₆ alkyl or R₃ is CONR₇ R₈ by conventional esterification or amination respectively.

Z¹ when other than Z may have a hydrogenolysable protecting group which is benzyl optionally substituted by one or two groups as defined for R₁ and R₂. Such benzyl groups may, for example, be removed, when R₁ or R₂ is not halogen, by conventional transition metal catalysed hydrogenolysis to give compounds of the formula (X): ##STR10## wherein Z₂ is of formula (d) or (e): ##STR11## wherein the variables are as defined in formula (I).

This invention also provides a further process for the preparation of a compound of the formula (I) which comprises N-alkylating a compound of formula (X), and optionally forming a pharmaceutically acceptable salt, of the resulting compound of the formula (I).

In this further process of the invention `N-alkylation` comprises the substitution of the N-atom depicted in formula (X) by any group R₄ /R₅ as hereinbefore defined. This may be achieved by reaction of the compound of formula (X) with a compound R₄ Q₄ or R₅ Q₄ wherein R₄ and R₅ are as hereinbefore defined and Q₄ is a leaving group.

Suitable values for Q₄ include groups displaced by nucleophiles such as Cl, Br, I, OSO₂ CH₃ or OSO₂ C₆ H₄ pCH₃, and when R₄ /R₅ is methyl, Q₄ is OSO₃ CH₃.

Favoured values for Q₄ include Cl, Br and I.

The reaction may be carried out under conventional alkylation conditions for example in an inert solvent such as dimethylformamide in the presence of an acid acceptor such as potassium carbonate. Generally the reaction is carried out at non-extreme temperature such as at ambient or slightly above.

Alternatively, `N-alkylation` may be effected under conventional reductive alkylation conditions when the group R₄ or R₅ in the compound of formula (I) contains a methylene group adjacent to the N-atom in the bicycle.

Interconverting R₄ or R₅ in the compound of the formula (X) before coupling with the compound of the formula (V) is also possible. Such interconversions are effected conveniently under the above conditions. It is desirable to protect any amine function with a group readily removable by acidolysis such as a C₂₋₇ alkanoyl group, before R₄ /R₅ interconversion.

When R₄ or R₅ in the compound of formula (VI) contains a methylene group adjacent to the N-atom in the bicycle it is often convenient in the preparation of such a compound of formula (VI) to prepare the corresponding compound wherein the methylene group is replaced by --CO--, or for R₄ or R₅ is methyl, where the methyl group is replaced by esterified carboxyl. Such compounds may then be reduced using a strong reductant such as lithium aluminium hydride to the corresponding compound of formula (VI).

The compounds of formula (V) and (VI) are known or are preparable analogously to, or routinely from, known compounds.

Compounds of the formula (VI) wherein Z is of formula (c) may be prepared as described in European Patent Publication No. 115933 or by analogous methods thereto.

Compounds of the formula (X) are novel and form an aspect of the invention.

It will be realised that in the compound of the formula (I) the --CO--L-- linkage may have an endo or exo orientation with respect to the ring of the bicyclic moiety to which it is attached. A mixture of endo and exo isomers of the compond of the formula (I) may be synthesised non-stereospecifically and the desired isomer separated conventionally therefrom e.g. by chromatography; or alternatively the endo and exo isomer may if desired by synthesised from the corresponding endo or exo form of the compound of the formula (VI).

Pharmaceutically acceptable salts of the compounds of this invention may be formed conventionally. The salts may be formed for example by reaction of the base compound of formula (I) with a pharmaceutically acceptable organic or inorganic acid.

The compounds of the present invention are 5-HT antagonists and it is thus believed may generally be used in the treatment or prophylaxis of migraine, cluster headaches and trigeminal neuralgia; and also as anti-emetics, in particular that of preventing vomiting and nausea associated with cancer therapy, and motion sickness. Examples of such cancer therapy include that using cytotoxic agents, such as cisplatin, doxorubicin and cyclophosphamide, particularly cisplatin; and also radiation treatment. Compounds which are 5-HT antagonists may also be of potential use in the treatment of CNS disorders such as anxiety and psychosis; arrhythmia, obesity and gastrointestinal disorders such as irritable bowel syndrome.

The invention also provides a pharmaceutical composition comprising a compound of formula (I), or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.

Such compositions are prepared by admixture and are suitably adapted for oral or parenteral administration, and as such may be in the form of tablets, capsules, oral liquid preparations, powders, granules, lozenges, reconstitutable powders, injectable and infusable solutions or suspensions or suppositories. Orally administrable compositions are preferred, since they are more convenient for general use.

Tablets and capsules for oral administration are usually presented in a unit dose, and contain conventional excipients such as binding agents, fillers, diluents, tabletting agents, lubricants, disintegrants, colourants, flavourings, and wetting agents. The tablets may be coated according to well known methods in the art, for example with an enteric coating.

Suitable fillers for use include cellulose, mannitol, lactose and other similar agents. Suitable disintegrants include starch, polyvinylpolypyrrolidone and starch derivatives such as sodium starch glycollate. Suitable lubricants include, for example, magnesium stearate.

Suitable pharmaceutically acceptable wetting agents include sodium lauryl sulphate. Oral liquid preparations may be in the form of, for example, aqueous or oily suspensions, solutions, emulsions, syrups, or elixirs, or may be presented as a dry product for reconstitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, for example sorbitol, syrup, methyl cellulose, gelatin, hydroxyethylcellulose, carboxymethylcellulose, aluminium stearate gel or hydrogenated edible fats, emulsifying agents, for example lecithin, sorbitan monooleate, or acacia; non-aqueous vehicles (which may include edible oils), for example, almond oil, fractionated coconut oil, oily esters such as esters of glycerine, propylene glycol, or ethyl alcohol; preservatives, for example methyl or propyl p-hydroxybenzoate or sorbic acid, and if desired conventional flavouring or colouring agents.

Oral liquid preparations are usually in the form of aqueous or oily suspensions, solutions, emulsions, syrups, or elixirs or are presented as a dry product for reconstitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, emulsifying agents, non-aqueous vehicles (which may include edible oils), preservatives, and flavouring or colouring agents.

The oral compositions may be prepared by conventional methods of blending, filling, or tabletting. Repeated blending operations may be used to distribute the active agent throughout those compositions employing large quantities of fillers. Such operations are, of course, conventional in the art.

For parenteral administration, fluid unit dose forms are prepared containing a compound of the present invention and a sterile vehicle. The compound, depending on the vehicle and the concentration, can be either suspended or dissolved. Parenteral solutions are normally prepared by dissolving the compound in a vehicle and filter sterilising before filling into a suitable vial or ampoule and sealing. Advantageously, adjuvants such as a local anaesthetic, preservatives and buffering agents are also dissolved in the vehicle. To enhance the stability, the composition can be frozen after filling into the vial and the water removed under vacuum.

Parenteral suspensions are prepared in substantially the same manner except that the compound is suspended in the vehicle instead of being dissolved and sterilised by exposure of ethylene oxide before suspending in the sterile vehicle. Advantageously, a surfactant or wetting agent is included in the composition to facilitate uniform distribution of the compound of the invention.

The invention further provides a method of treatment or prophylaxis of migraine, cluster headache, trigeminal neuralgia and/or emesis in mammals, such as humans, which comprises the administration of an effective amount of a compound of the formula (I) or a pharmaceutically acceptable salt thereof.

An amount effective to treat the disorders hereinbefore described depends on the relative efficacies of the compounds of the invention, the nature and severity of the disorder being treated and the weight of the mammal. However, a unit dose for a 70 kg adult will normally contain 0.5 to 1000 mg for example 1 to 500 mg, of the compound of the invention. Unit doses may be administered once or more than once a day, for example, 2, 3 or 4 times a day, more usually 1 to 3 times a day, that is in the range of approximately 0.001 to 50 mg/kg/day, more usually 0.002 to 25 mg/kg/day.

No adverse toxicological effects are indicated at any of the aforementioned dosage ranges.

The invention also provides a compound of formula (I) or a pharmaceutically acceptable salt thereof for use as an active therapeutic substance, in particular for use in the treatment of migraine, cluster headache, trigeminal neuralgia and/or emesis.

The following Examples illustrate the preparation of compounds of formula (I).

EXAMPLE 1

(endo)-N-(8-Methyl-8-azabicyclo[3.2.1]oct-3-yl)-N'-(2-methoxy-pyrid-3-yl)urea (E1) ##STR12##

To a stirred solution of phosgene (12.5% in toluene, 7.3 ml), in CH₂ Cl₂ (80 ml) at room temperature was added 3-amino-2-methoxypyridine (1.0 g) in CH₂ Cl₂ (5 ml). After stirring the reaction mixture for 10 min., triethylamine (2.5 ml) was added and the stirring continued for a further 10 mins. A solution of (endo)-8-methyl-8-azabicyclo[3.2.1]octan-3-amine (1.13 g) in CH₂ Cl₂ (5 ml) was then added and the whole stirred for 3 h. The solution was washed with sat. NaHCO₃ solution, dried (K₂ CO₃) and evaporated to dryness. Purification of the residue by column chromatography (T.L.C. grade alumina, CH₂ Cl₂) afforded the title compound (E1) (1.3 g) m.p. 197°-200° C. (CH₂ Cl₂ /Et₂ O).

    ______________________________________                                         .sup.1 H--NMR (δ, CDCl.sub.3, 270 MHz)                                                     8.33     (dm, 1H)                                                              7.76     (dm, 1H)                                                              6.96     (brs, 1H)                                                             6.86     (dd, 1H)                                                              5.36     (brd, 1H)                                                             4.05-3.90                                                                               (m, 4H including                                                               3.98, s, 3H)                                                          3.28     (brs, 2H)                                                             2.17-2.02                                                                               (m, 2H)                                                               1.90-1.80                                                                               (m, 2H)                                                               1.71     (d, 2H)                                             ______________________________________                                    

EXAMPLE 2 (endo)-N-(8-Methyl-8-azabicyclo[3,2,1]oct-3-yl)-N'-(3-methoxy-pyrid-2-yl)urea (E2) ##STR13##

A solution of 2-amino-3-methoxypyridine (0.55 g) and 1,1'-carbonyldiimidazole (0.86 g) in xylene (50 ml) was stirred at room temperature for 1 h. A solution of (endo)-8-methyl-8-azabicyclo[3,2,1]octan-3-amine (0.8 g) in xylene (10 ml) was added and the whole heated to reflux for 2 h. The reaction mixture was evaporated to dryness and the residue partitioned between CHCl₃ (100 ml) and saturated NaHCO₃ solution (50 ml). The CHCl₃ extract was removed, dried (K₂ CO₃) and evaporated to dryness. The residue was purified by column chromatography (Al₂ O₃, CH₂ Cl₂ -CHCl₃), to give the title compound (0.9 g) m.p. 178°-80°.

    ______________________________________                                         .sup.1 H--NMR (δ, CDCl.sub.3)                                            ______________________________________                                         10.12        (d, 1H)                                                           7.76         (dm, 1H)                                                          7.32         (brs, 1H)                                                         7.04         (dm, 1H)                                                          6.85         (dd, 1H)                                                          4.13         (q, 1H)                                                           3.86         (s, 3H)                                                           3.22         (brs, 2H)                                                         2.40-2.00    (m, 9H including 2.32, s, 3H)                                     1.77         (d, 2H)                                                           ______________________________________                                    

EXAMPLE 3 (endo)-N-(8-Methyl-8-azabicyclo[3,2,1]oct-3-yl)-N'-(3-methoxythiophen-2-yl)urea (E3) ##STR14##

To a stirred solution of 3-methoxythiophene 2-carboxylic acid (0.5 g) in dry THF (20 ml) and triethylamine (0.44 ml) was added diphenylphosphoryl azide (0.7 ml) at 0° C. The mixture was stirred at room temperature for 2 h, then heated to reflux for 1 h. The solution was cooled to 0° C. and (endo)-8-methyl-8-azabicyclo[3,2,1]octan-3-amine (0.44 g) was added. The reaction mixture was then stirred at room temperature for 3 h, evaporated to dryness and the residue partitioned between CH₂ Cl₂ and saturated NaHCO₃ solution. Acid-base extraction of the separated CH₂ Cl₂ layer gave the crude product which was purified by column chromatography (Al₂ O₃, CH₂ Cl₂ -CHCl₃) to give the title compound (0.2 g)

    ______________________________________                                         .sup.1 H--NMR (δ, CDCl.sub.3)                                            ______________________________________                                         7.00-6.85   (brs, 1H superimposed on d, 1H)                                    6.78        (d, 1H)                                                            5.56        (brd, 1H)                                                          3.98        (q, 1H)                                                            3.85        (s, 3H)                                                            3.12        (brs, 2H)                                                          2.29        (s, 3H)                                                            2.28-2.12   (m, 2H)                                                            2.10-1.95   (m, 2H)                                                            1.75-1.60   (m, 4H)                                                            ______________________________________                                    

EXAMPLE 4 (endo)-N-(8-Methyl-8-azabicyclo[3,2,1]oct-3-yl)-N'-(2-methoxythiophen-3-yl)urea (E4) ##STR15##

Following the procedure outlined in Example 3, 2-methoxythiophene-3-carboxylic acid (0.4 g) was converted to the title compound (0.19 g). m.p. 224°-6° (dec)

    ______________________________________                                         .sup.1 H--NMR (δ, d.sup.6 -DMSO)                                         ______________________________________                                         8.10              (s, 1H)                                                      7.30              (d, 1H)                                                      6.71              (d, 1H)                                                      6.35              (d, 1H)                                                      3.83              (s, 3H)                                                      3.71              (q, 1H)                                                      2.97              (brs, 2H)                                                    2.16              (s, 3H)                                                      2.77-2.06         (m, 6H)                                                      1.46              (d, 2H)                                                      ______________________________________                                    

EXAMPLE 5 (endo)-N-(8-Methyl-8-azabicyclo[3,2,1]oct-3-yl)-N'-(4-methoxythiophen-3-yl)urea (E5) ##STR16##

A stirred solution of 4-methoxythiophen-3-carboxylic acid azide (0.42 g) in dry toluene (10 ml) was heated to reflux under N₂ for 30 min. On cooling, (endo)-8-methyl-8-azabicyclo[3,2,1]octan-3-amine (0.32 g) was added and the reaction stirred at room temperature for 40 mins. The precipitate was collected and purified by column chromatography (Al₂ O₃, CH₂ Cl₂ -10% MeOH/CHCl₃) to give the title compound (0.08 g) m.p. 225°-7° C. (dec)

    ______________________________________                                         .sup.1 H--NMR (δ, d.sup.6 -DMSO)                                         ______________________________________                                         8.26              (s, 1H)                                                      7.29              (d, 1H)                                                      6.59              (d, 1H)                                                      6.25              (d, 1H)                                                      3.90              (s, 3H)                                                      3.86              (q, 4H)                                                      3.06              (brs, 2H)                                                    2.23              (s, 3H)                                                      2.20-1.85         (m, 6H)                                                      1.60              (d, 2H)                                                      ______________________________________                                    

EXAMPLE 6 (endo)-N-(8-Methyl-8-azabicyclo[3,2,1]oct-3-yl)-N'-(2-methoxycarbonylthiophen-3-yl)urea (E6) ##STR17##

Following the procedure outlined in Example 1, methyl 3-amino-thiophene-2-carboxylate (0.63 g) was converted to the title compound (0.82 g). m.p. 141°-2° C.

    ______________________________________                                         .sup.1 H--NMR (δ, CDCl.sub.3)                                            ______________________________________                                         9.40        (brs, 1H)                                                          7.98        (d, 1H)                                                            7.42        (d, 1H)                                                            5.05        (d, 1H)                                                            4.05-3.95   (m, 1H)                                                            3.88        (s, 3H)                                                            3.34-3.24   (brs, 2H)                                                          2.44-1.74   (m, 11H including 2.40, s, 3H)                                     ______________________________________                                    

PHARMACOLOGY Antagonism of the von Bezold-Jarisch reflex

The compounds were evaluated for antagonism of the von Bezold-Jarisch reflex evoked by 5-HT in the anaesthetised rat according to the following method:

Male rats 250-350 g, were anaesthetised with urethane (1.25 g/kg intraperitoneally) and blood pressure and heart rate recorded as described by Fozard J. R. et al., J. Cardiovasc. Pharmacol. 2, 229-245 (1980). A submaximal dose of 5-HT (usually 6 μg/kg) was given repeatedly by the intravenous route and changes in heart rate quantified. Compounds were given intravenously and the concentration required to reduce the 5-HT-evoked response to 50% of the control response (ED₅₀) was then determined.

The results were as follows:

    ______________________________________                                         Compound     ED.sub.50 μg/kg i.v.                                           ______________________________________                                         1            7.5                                                               3            1.0                                                               5            2.0                                                               ______________________________________                                     

I claim:
 1. A compound of formula (I), or a pharmaceutically acceptable salt thereof: ##STR18## wherein: Het is monocyclic heteroaryl having two adjacent carbon atoms, a and b, depicted in formula (I) selected from the group consisting of pyridine, pyrimidine, pyrazine, pyrrole, imidazole, thiophene, furan, oxazole and thiazole;R₁ and R₂ are independently selected from hydrogen, halogen, CF₃, C₁₋₆ alkyl and C₁₋₆ alkoxy; R₃ is hydroxy, C₁₋₆ alkoxy, C₃₋₇ alkenyl-methoxy, phenoxy or phenyl C₁₋₄ alkoxy in which either phenyl moiety may be substituted by one or two C₁₋₆ alkyl, C₁₋₆ alkoxy or halo; CO₂ R₆ wherein R₆ is hydrogen or C₁₋₆ alkyl, CONR₇ R₈ or SO₂ NR₇ R₈ wherein R₇ and R₈ are independently hydrogen or C₁₋₆ alkyl or together are C₄₋₆ polymethylene, NO₂, (CH₂)_(m) OR₉ wherein m is 1 or 2 and R₉ is C₁₋₆ alkyl or S(O)_(n) R₁₀ wherein n is 0, 1 or 2 and R₁₀ is C₁₋₆ alkyl; L is NH or O; Z is a group of formula (a), (b) or (c): ##STR19## wherein n is 2 or 3; p is 1 or 2; q is 1 to 3; r is 1 to 3; and R₄ or R₅ is C₁₋₄ alkyl.
 2. A compound according to claim 1 of formula (II) ##STR20## wherein Het, R₁, R₂, R₃, R₄, n and L are as defined in claim
 1. 3. A compound according to claim 1 wherein Het is pyridine or thiophene.
 4. A compound according to claim 1 wherein R₁ and R₂ are both hydrogen and wherein R₃ is methoxy, ethoxy, propoxy, methoxycarbonyl, ethoxycarbonyl or dimethylaminosulphonyl.
 5. A compound according to claim 1 wherein L is NH.
 6. A compound selected from the group consisting of:(endo)-N-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-N'-(2-methoxy-pyrid-3-yl)urea, (endo)-N-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-N'-(3-methoxy-pyrid-2-yl)urea, (endo)-N-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-N'-(3-methoxythiophen-2-yl)urea, (endo)-N-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-N'-(2-methoxythiophen-3-yl)urea, (endo)-N-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-N'-(4-methoxythiophen-3-yl)urea, (endo)-N-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-N'-(2-methoxycarbonylthiophen-3-yl)urea,and pharmaceutically acceptable salts of any of the foregoing.
 7. A pharmaceutical composition for use in the treatment of migraine, cluster headache, trigeminal neuralgia or emesis in mammals, comprising an effective amount of a compound according to claim 1, and a pharmaceutically acceptable carrier.
 8. A method of treatment of migraine, cluster headache, trigeminal neuralgia or emesis, in mammals, which method comprises the administration of an effective amount of a compound according to claim
 1. 